The Paintball Radarchron is a hand held doppler radar velcoity sensor that measures the speed of the paintball as it is shot from the marker. I was able to buy this particular one for $43 shippped on ebay. Its pretty simple to use due to the 1 button operation. Press the buttton once and hold the radarchron 1/2 inch under the barrel. It will read as a single number then flash to a 2 digit number then back to the first number. Example 275fps will read 2, then 75, then 2 again. Dont know why they just wouldnt make a 3 digit display for it, but then again this is much cheaper that the big red $200 one found at the local fields. Its nice that it has case but i never use the straps for it. This is great to have at home the night before u hit the field. U can pop off a few rounds at home making sure your fps is right before u hit the field the next morning. I also do alot of tinkering with my markers trying different bolts, poppits, rams etc. So this let me see the difference in using different aftermarket parts which is a great help. If you dont paintball alot meaning your going once or twice a year you'll have no need for it, but if u go often its great to have. No one likes waiting for 3 or 4 people using the big red radar at the field.